Possible Clues:

• Six Beethoven string works
• Classical-music movements
• The Dixie Chicks and others
• Some lounge groups
• Minuet parts
• Small groups
• The Police and The Bee Gees, for two
• The Bee Gees and Peter, Paul and Mary, e.g.
• Some Brahms works
• Nirvana and Destiny's Child